Setting Boundary Conditions and Values

The only additional boundary specifications needed for this analysis are the emissivities and reflectivities of the boundaries surrounding the fluid region. The vertical and horizontal walls will be assigned an emissivity of 0.5 and a reflectivity of 0.5. The solid-fluid interface will be assigned an emissivity of 0.2 and a reflectivity of 0.8. Kirchoff's Law (emissivity = absorptivity) is assumed by the solver for this case and you should also check that, for each boundary, emissivity + reflectivity = 1, as is the case here.

The emissivity and reflectivity of the solid-fluid interface must be specified at the Air-Interface [In-place 1] boundary, not the Air-Interface boundary, as the latter became defunct when the interface was created (see Creating Interfaces in the Heated Fin Tutorial).

Note that it is not necessary to set the emissivity and reflectivity for boundaries in the solid region since we are only intending to model radiation through the air. This is a reasonable approach as the fin is assumed to be opaque.